Glass windows are broadly used in automobiles. Some of the glass windowpanes, specifically those mounted stationarily, are equipped with plastic gaskets around their periphery to provide environmental seal. A convenient method of installing these plastic gaskets on the glass windowpanes is to mold in place the plastic gaskets around the periphery of the glass windowpanes by a plastic injection molding/encapsulation process.
In a typical plastic injection molding/encapsulation process, a set of matched metal molds is used. The molds are designed such that a glass workpiece can be held securely in the middle of the molds while the periphery of the glass workpiece is exposed to the mold cavity. The mold cavity is provided such that it is in fluid communication with an injection gating device located on the side of the mold adjacent to the parting line of the two molds. When molten plastic material is injected into the mold cavity, it rapidly flows around the periphery of the glass workpiece filling the mold cavity and thus providing a plastic gasket around the perimeter of the glass workpiece.
The glass windowpanes used in automobiles are normally made from tempered glass. Frequently, when a glass workpiece is loaded into the mold apparatus and clamped between the upper and the lower mold halves, the clamping pressure placed on the glass workpiece would break and shatter the workpiece. We have observed a unique property of tempered glass is that it always breaks in a consistent and uniform manner. This is caused by the tremendous amount of tension and compression in the glass in its normal unstressed state. During breakage of a piece of tempered glass, the cracks produced in the glass always run perpendicular to the glass surface evenly along the entire surface area of the glass.
If the glass workpiece breaks after the mold is closed and clamped together and such breakage is not detected, the subsequent injection of the molten plastic material into the mold would cause severe damage to the mold cavity. Since the surface area of the mold cavity is normally highly polished in order to produce a high gloss finish on the plastic gasket, any scratch of such highly polished surface would require significant amount of time and labor to remove the mold from the injection molding machine and to repair the mold. This type of repair causes a significant amount of downtime in the production of plastic encapsulated glass workpieces.
It is, therefore, an object of the present invention to provide a mold apparatus for the plastic injection molding/encapsulation of plastic materials around a glass workpiece equipped with an optical sensing device for glass breakage such that the subsequent plastic injection process can be stopped to avoid damages to the mold apparatus.
It is another object of the present invention to provide a mold apparatus for the plastic injection molding/encapsulation of plastic materials around a glass workpiece equipped with an optical sensing device for glass breakage such that any cracks in the glass workpiece may be detected and an automatic shutoff device may be triggered to stop the plastic injection process to avoid any damages to the surface of the mold cavity.
It is a further object of the present invention to provide a mold apparatus for the plastic injection molding/encapsulation of plastic materials around a glass workpiece equipped with an optical sensing device for glass breakage that is sensitive to detect cracks in tinted glass and glass workpieces contaminated with fingerprints and dirt such that an automatic shutoff device may be triggered to stop the plastic injection process to avoid damages to the mold cavity.